1. Field of the Invention
This invention relates to a television interphone apparatus provided for communication between building entrances and individual apartments of the building, along with transmission of visitor's pictures to a monitor mounted on the wall of the apartment.
2. Description of the Prior Art
A television interphone monitor used for entrance monitoring and communication is mounted on a wall inside the apartment and is wired via multi-core cables for connecting to each other different elements of the system, such as a microphone and speaker wires, a coax cable for video signals, a door release wire, a calling wire and an alarm wire. Whenever a more complex system is installed such as for multi-entrances or as concierge station systems the wiring becomes very complex and costly.
Such a television interphone monitor unit mounted on the wall of the individual apartment requires an individual power supply having sufficient capacity to power the monitor and the interphone. Since multi-television interphone monitor units are assembled into an apartment block, such system requires extensive wiring and cabling along with a large number of power supplies and heavy power wires for connecting many power supplies to many television monitor units, which is laborious and costly.
Such television interphone monitors may be powered from a central power supply which requires a large power capacity and exclusive heavy gauge wires to connect the power supply to each television interphone monitor. It would be advantageous to feed the power through a signal transmission line. However, as the television monitor circuits consume most of the power needed for operating the television interphone monitor unit and as the monitor operates at random, the current consumed by the television interphone monitor is not constant and therefore if the power to the television interphone monitor is fed through the transmission line it will disturb the flow of signals.
On the other hand, an apparatus for powering television cameras via the camera transmission line along with transmitting audio, I.D. and control signals through a common transmission line is disclosed in copending U.S. patent application Ser. No. 08/803,616 dated Feb. 21, 1997.